Electroinitiated cationic polymerization of styrene

A constant controlled current was passed through a solution of styrene in methylene chloride containing a tetraalkylammonium salt as supporting electrolyte. Reproducible rates of polymerization were initiated by the electrochemical techniques employed and the kinetics of the reaction were investigated. Sigmoidal curves of conversion versus time were observed. A kinetic relationship of the form In ([M₀]/[M]) = ½ Kt² was derived on the basis of simple assumptions regarding the mechanism and fitted the data accurately. The rate constants obtained were compared to others reported, and the influences of ion association on the values of the rate constants obtained are discussed. The reactions were decreased in rate by a reversal of polarity of the electrodes. However, the stoichiometry of the production of active centers and of their destruction was not ideal, in that each electron did not result in the initiation of a polymer chain.     

Electroinitiated cationic polymerization of styrene by direct electron transfer

We have studied by cyclic voltammetry the mechanisms of electron transfer and peak potentials of eleven alkenes, propylene oxide, propylene sulfide, and carbon disulfide. We have also studied the cationic polymerization of styrene in acetonitrile solution initiated by controlled potential electrolysis at the anodic peak potential of styrene. The electrolyte used was tetrabutylammonium fluoborate, which was not electroactive at the electrolysis potential, and the reference electrode was a Ag⁰/Ag⁺ electrode. The electrochemical studies show that direct electron transfer from styrene is the initiation steps. Plots of reacted monomer concentrations versus time are sigmoidal curves. The propagation rate constant was found from a kinetic relationship based on an autocatalytic reaction. The activation energy is 15.6 kcal/mole at 20°C. The current behavior and effect of stirring on polymerization rate suggest that the growth of polymer takes place partially on the electrode surface.     

Electroinitiated polymerization of styrene in dimethylsulphate

The electroinitiated polymerization of styrene in tetrabutylammonium perchlorate-dimethylsulphate solutions has been investigated. Polystyrene of low molecular weight is formed cationically through a direct monomer oxidation to the radical cation. Kinetic as well as mechanistic considerations for this system are made difficult by a number of factors: (a) the polymer is to a large extent insoluble in dimethylsulphate; (b) side reactions of both monomer and polymer tend to decrease the yields and therefore the calculated k_p values: (c) the supporting electrolyte concentration tends to affect the ionic equilibria in solution, so again influencing the k_p values.

A polymer degradation, found for polystyrene in LiClO₄-propylene carbonate solutions, was again noted and attributed to the effect of the current on the polymer covering the anode. The polymerization has no true termination, the only chain-stopping reactions being those giving rise to chain transfer.     

Microemulsion polymerization of styrene in the presence of a cationic emulsifier

The principal subject discussed in the current paper is the radical polymerization of styrene in the three- and four component microemulsions stabilized by a cationic emulsifier. Polymerization in the o/w microemulsion is a new polymerization technique which allows to prepare the polymer latexes with the very high particle interface area and narrow particle size distribution. Polymers formed are very large with a very broad molecular weight distribution. In emulsion and microemulsion polymerizations, the reaction takes place in a large number of isolated loci dispersed in the continuous aqueous phase. However, in spite of the similarities between emulsion and microemulsion polymerization, there are large differences caused by the much larger amount of emulsifier in the latter process. In the emulsion polymerization there are three rate intervals. In the microemulsion polymerization only two reaction rate intervals are commonly detected: first, the polymerization rate increases rapidly with the reaction time and then decreases steadily. Essential features of microemulsion polymerization are as follows: (1) polymerization proceeds under non-stationary state conditions; (2) size and particle concentration increases throughout the course of polymerization; (3) chain-transfer to monomer/exit of transferred monomeric radical/radical re-entry events are operative; and (4) molecular weight is independent of conversion and distribution of resulting polymer is very broad. The number of microdroplets or monomer-starved micelles at higher conversion is high and they persist throughout the reaction. The high emulsifier/water ratio ensures that the emulsifier is undissociated and can penetrate into the microdroplets. The presence of a large amount of emulsifier strongly influences the reaction kinetics and the particle nucleation. The mixed mode particle nucleation is assumed to govern the polymerization process. At low emulsifier concentration the micellar nucleation is dominant while at a high emulsifier concentration the interaction-like homogeneous nucleation is operative. Furthermore, the paper is focused on the initiation and nucleation mechanisms, location of initiation locus, and growth and deactivation of latex particles. Furthermore, the relationship between kinetic and molecular weight parameters of the microemulsion polymerization process and colloidal (water/particle interface) parameters is discussed. In particular, we follow the effect of initiator and emulsifier type and concentration on the polymerization process. Besides, the effects of monomer concentration and additives are also evaluated.     

Radiation-induced cationic dimerization and polymerization of styrene in methylene chloride solution. I

Radiation-induced polymerization of styrene in methylene chloride solution or bulk system was investigated to explain the initiation mechanism of cationic polymerization. It was found that high energy radiation produces polymers and dimers. The main dimers were identified as trans-1,2-diphenylcyclobutane, 1-phenyl-1,2,3,4-tetrahydronaphthalene, and 1-phenyl-1,2-dihydronaphthalene. The dimerization procedure was cationic in a pattern similar to that obtained in photoexcited EDA systems. It was shown clearly by product analysis that the bonded dimer cation radical intermediate, which was assumed to be an initiating species of the cationic polymerization, was produced in a radiation-induced polymerization system. The observed polymerization was composed of two types; cationic and radical, the latter initiated by radical species.     

Photodegradation of polyethylene in the presence of ferric chloride

Effects of ferric chloride (FeCl₃) on photodegradation of high-density polyethylene (PE) were investigated by using ESR and infrared spectrometry. In the system with irradiation at light of λ > 220 nm, PE irradiated at 77°K yielded an 8-line spectrum, the intensity of which was markedly weakened by using FeCl₃ with the sample, indicating a distinct depression of radical formation. On the other hand, PE with the use of FeCl₃ yielded radicals under irradiation only with light of λ > 300 nm, showing a singlet spectrum with a line width of 15 gauss. For photooxidized PE, almost the same effect of FeCl₃ was observed. On irradiation at room temperature, PE samples with and without FeCl₃ showed a singlet spectrum with line widths of 15 and 25 gauss, respectively. On the other hand, the unsaturated double bond contained in a small amount in PE sample was observed by infrared study to be decreased with photoirradiation; however, the decrease was sharply depressed with the addition of FeCl₃ to the sample. The degradation of carbonyl group in a photooxidized sample was markedly affected by photoirradiation, and the decay was obviously reduced for the sample on addition of FeCl₃. It is concluded that FeCl₃ works upon photodegradation of PE to enhance the Norrish type II reaction and to accelerate the formation of unsaturated double bond in the chain.     

Synthesis of butyl rubber by cationic polymerization in methyl chloride in the presence of alkyl chlorides

The copolymerization of isobutylene with isoprene in methyl chloride in the presence of a catalytic system based on aluminum chloride and modified with alkyl chlorides was studied systematically.     

Effect of formaldehyde on the cationic polymerization of styrene

Polymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady-state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady-state rate of polymerization followed the equation: where [C]₀ and [F]₀ are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k₁, k₂, and k₃ are constants. It has been assumed that the chain-transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain-transfer constant for the added formaldehyde has been determined to be 1.63.     

Electroinitiated polymerization of allylphenylether

Electroinitiated polymerization of allylphenylether via constant potential electrolysis was accomplished in acetonitrile at room temperature. Electroinitiated polymerization of the monomer yielded insoluble polymers on the surface of the anode together with soluble polymers in the bulk solution. The structural analyses of the polymers were done by ¹H-NMR and FTIR spectroscopy. ¹H-NMR results showed that monosubstituted aromatic ring of the monomer becomes tri-substituted during the electroinitiated polymerization. The effect of monomer concentration and applied potential on the rate of electroinitiated polymerization were also studied. © 1995 John Wiley & Sons, Inc.     

Anionic polymerization of styrene in the presence of pyridine

An interesting effect of pyridine on the anionic polymerization of styrene in THF is described. Pyridine forms a complex with living polystyrene and greatly slows the polymerization rate without changing the degree of polymerization. From kinetic and spectroscopic studies, it was clear that there exist two active species in this system and the complex between living polystyrene and pyridine was of the 1:1 type, which itself had a weak ability to grow. The formation constant of the complex K was found to be about 4 × 10⁵ l./mole. The effect of substituted pyridine was also studied and the nature of the complex was discussed.     

Effects of triphenylsulfonium hexafluorophosphate in the radiation-induced cationic polymerization of styrene

Radiation-induced cationic polymerization of styrene was studied in methylene chloride in the presence of triphenylsulfonium hexafluorophosphate. Acceleration in polymerization and an increase in molecular weight at a low temperature (?78°C) were observed in the presence of triphenylsulfonium salt. A study of pulse radiolysis revealed that both effects are due mainly to PF^?6, which forms ion pairs with the cationic species involved in the polymerization.     

Electroinitiated polymerization of 2-vinylnaphthalene

As part of a program to extend the range of donor–acceptor-initiated polymerization processes, the electroinitiation of 2-vinylnaphthalene in a zinc chloride–sulfolane solution has been studied. Good conversion yields of well-characterized (NMR, IR, GPC, elemental analysis) poly(vinylnaphthalene) were obtained with the process showing several mechanistic similarities to other donor–acceptor salt electropolymerization systems.     

Electroinitiated polymerization of butadiene sulfone

Electroinitiated polymerization of butadiene sulfone was achieved by direct electron transfer in acetonitrile—tetrabutylammonium fluoroborate system by controlled potential electrolysis technique. High conversions were obtained at reasonable temperatures and polymerization times. The polymer was found to be composed of linear segments along with some cyclic units. The effect of monomer concentration, temperature, and polymerization potential on the rate of polymerization was investigated. Temperature and polymerization potential have positive effects on the rate of polymerization. The effect of ultrasonic vibration was also investigated by conducting electrolyses at different monomer concentrations in the presence and absence of ultrasonic vibration. It was observed that the rate of polymerization increases significantly in the presence of ultrasonic vibration. The inverse relationship between the rate of polymerization and monomer concentration was observed in presence and absence of ultrasonic vibration.     

Gamma-ray induced polymerization of styrene in the presence of methanol

The kinetics and molecular weight distributions (MWD) of the gamma-ray induced polymerization of styrene in methanol were studied at 35°C, at low conversions and over a dose rate range of 2.76 × 10³ to 2.74 × 10⁴ rad/hr. The data obtained at low initial methanol content agreed with previously obtained results and the MWD of the polystyrene formed yielded a single unimodal peak with M?_n in the range of 35,000–480,000. However, at high initial methanol content and low dose rates, at least three peaks were clearly discernible over wide molecular weight distributions. The existence of these peaks is related to the kinetic data and the formation of three distinguishable regions in the polymerization system.